1. Light Intensity
D. Crowley, 2008

2. Friday, April 21, 2017
Light Intensity
To understand how light intensity affects photosynthesis

3. carbon dioxide + water  glucose + oxygen
Talking
Why can you argue that it is good for your plants to talk to them?!
Remember, when plants grow they do so via photosynthesis – for this to occur plants need carbon dioxide, water and light (and when you speak, you exhale carbon dioxide)!
chlorophyll light energy
carbon dioxide + water  glucose + oxygen
6CO2 + 6H2O  C6H12O6 + 6O2

4. Rate Of Photosynthesis
What can affect the rate of photosynthesis?
Photosynthesis needs carbon dioxide, water and light (as well as a variety of nutrients)
If any of these are taken away, they become a limiting factor of photosynthesis – reducing the amount of photosynthesis which can take place…

5. Light Intensity Experiment
How could you measure how light intensity affects the rate of photosynthesis?
Hydrogen carbonate indicator reacts when carbon dioxide is present: -
In normal atmospheric conditions, the indicator is orange/red
When there is lots of carbon dioxide the indicator is yellow
When there is not much carbon dioxide the indicator is purple
So we can set up an experiment, changing the light intensity, and then measure the hydrogen carbonate indicator to see how the CO2 levels vary…

6. Experiment Take 2 similar pieces of elodea
Place 1 piece of elodea in a test tube and submerge with hydrogen carbonate indicator
Place 1 piece of black paper around the test tube, ensuring the top is sealed (use the rubber band)
Repeat this experiment, this time placing 1 piece of tracing paper around the test tube
Finally set up a control – a test tube with only hydrogen carbonate indicator and no elodea in it or paper around it!
Leave test tubes in a rack, by the window for >20 mins…

7. carbon dioxide + water  glucose + oxygen
Prediction
Write down your prediction – remember the photosynthesis equation and the colour changes of the hydrogen carbonate indicator…
carbon dioxide + water  glucose + oxygen
Hydrogen carbonate indicator reacts when carbon dioxide is present: -
In normal atmospheric conditions, the indicator is orange/red
When there is lots of carbon dioxide the indicator is yellow
When there is not much carbon dioxide the indicator is purple

8. Prediction
We should find the test tube with tracing paper (most light availability) should have photosynthesised the most – used up most of the CO2 so the indicator should be purple
The test tube with black paper should have stopped most of the light getting through, so not much photosynthesis would have taken place (respiration would actually increase CO2 content) – used least CO2 so the indicator should be yellow
Our control should remain orange/red